This invention relates to a process for preparing bis(silylorgano)amines by the catalyzed reaction of a cyanoorganosilane with hydrogen.
Bis(silylorgano)amines such as the bis(trialkoxysilyl)alkylamines, bis(alkoxyalkylsilyl)alkylamines, and the like are a commercially important class of secondary aminoorganosilanes. They are useful, inter alia, as coupling agents for glass onto plastic and metal surfaces, as bonding aids, as additives to phenolic binder/foundry mixtures, as adhesion promoters for vinyl plastisols, polyurethane elastomers and epoxy and acrylic-based inks.
U.S. Pat. No. 5,101,055 discloses the production of mixtures of bis- and tris(silylorgano)amines by the coupling reaction of a primary aminoorganosilane in the presence of palladium monoxide catalyst. Similarly, U.S. Pat. No. 4,526,996 discloses a process for coupling silyl nitrites with primary amines in the presence of catalytically active quantities of palladium on carbon at 160xc2x0 C. for 20 hours.
Several previously process patents also describe the hydrosilation of suitably substituted allyl amines as an alternative route to secondary amino silanes (U.S. Pat. No. 4,481,364 and DE 4,435,390).
U.S. Pat. No. 5,808,123 discloses the preparation of gamma-aminopropyltrialkoxysilanes as well as mixtures of primary and secondary aminosilanes by reacting gamma-chloropropyltrialkoxysilane with ammonia at elevated pressure and temperature. The reaction is preferably carried out at a temperature not exceeding 110xc2x0 C. in order to suppress the formation of secondary amine, i.e., bis(trialkoxysilylpropyl)amine, and increase the selectivity of the reaction for the primary amine, i.e., gamma-aminopropyltrialkoxysilane.
U.S. Pat. No. 5,117,024 describes a process for preparing a primary aminoorganosilane by the reaction of a cyanoorganosilane with hydrogen in the presence of a supported cobalt catalyst. In the improvement of this process disclosed in U.S. Pat. No. 6,242,627, the reaction of cyanoorganosilane with hydrogen to provide primary aminorganosilane is carried out using a sponge cobalt catalyst, preferably in the presence of an alkali metal hydroxide to inhibit or suppress the formation of secondary aminoorganosilane.
In accordance with the present invention, a process for preparing a bis(silylorgano)amine is provided which comprises reacting a cyanoorganosilane with hydrogen under hydrogenation conditions in the presence of a catalytically effective amount of hydrogenation catalyst selected from the group consisting of rhodium, ruthenium, palladium, and/or platinum.
Unlike the process of U.S. Pat. No. 5,101,055 which, in addition to bis(silylorgano)amine, produces large amounts of tris(silylorgano)amine, and the process of U.S. Pat. No. 5,808,123 which prefers to minimize the production of bis(silylorgano)amine and increase the yield of the primary amine, the process of the present invention provides high selectivity for the bis(silylorgano)amine coproducing at most a minor amount of primary aminoorganosilane, e.g., not exceeding about 35 weight percent of the total product amines, and even lesser amounts of tri(silylorgano)amine, e.g., not exceeding about 10 weight percent of the total product amines. And, in contrast to the processes of U.S. Pat. Nos. 5,117,024 and 6,242,627 both of which emphasize the production of primary aminoorganosilane, the major product produced by the process of the present invention is bis(silylorgano)amine.
The starting cyanoorganosilane reactant referred to herein is preferably one possessing the general formula
R13 SiR2CN
in which case the product bis(silylorgano)amine will conform to the general formula
(R13SiR2CH2)2NH
wherein each R1 group is independently selected from the group consisting of alkyl, aryl and alkoxy groups of up to about 10 carbon atoms with at least one R1 group being an aforesaid alkoxy group and each R2 is the same or different divalent hydrocarbon group containing no ethylenic unsaturation and having up to about 20 carbon atoms.
The R1 groups can be selected to be one or more of, for example, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, isobutyl, pentyl, dodecyl, methoxy, ethoxy, propoxy, isopropoxy, butoxy, phenyl or phenoxy. The R1 groups are preferably selected from the group consisting of methyl, methoxy, ethyl and ethoxy. Whatever the nature of the R1 groups, at least one of these groups must be an alkoxy group, e.g., any of the aforecited alkoxy groups.
Each divalent R2 group can be, for example, a divalent group of an alkane, cycloalkane, aromatic or aralkane compound. Thus, the divalent R2 groups can be, for example, the same or different linear or branched alkylene group such as methylene, ethylene, 1,2-propylene, 1,3-propylene, 2-methyl-1,3-propylene, 3-methyl-1,3-propylene, 3,3-dimethyl-1,3-propylene, ethylidene or isopropylidene, a cycloalkylene group such as cyclohexylene or cycloheptylene, an arylene group such as phenylene, tolylene, xylylene or naphthylene, or the divalent group xe2x80x94C6H4xe2x80x94R3xe2x80x94 in which R3 is methylene, ethylene, p ropylene, etc.
Examples of cyanoorganosilanes which can be hydrogenated by the process of this invention include 2-cyanoethyldimethylmethoxysilane, 2-cyanoethylmethyldimethoxysilane, 2-cyanoethyltrimethoxysilane, 2-cyanoethyltriethoxysilane, 2-cyanoethyldimethyl-ethoxysilane, 2-cyanoethylphenyldimethoxysilane, 2-cyanoethylphenyldiethoxysilane, 3-cyanomethyltriethoxysilane, 3-cyanopropyltrimethoxysilane, 3-cyanopropylmethyl-dimethoxysilane and 3-cyanopropylmethyldiethoxysilane.
It is preferred that the process herein be carried out in the presence of a molar excess of hydrogen, preferably two or more moles of hydrogen per mole of the selected cyanoorganosilane starting reactant. In general, the greater the amount of hydrogen present, the faster the reaction. Therefore, in a preferred mode of operating the process, hydrogen is added in excess at a concentration sufficient to maintain the pressure within the reactor within the range of from about 200 psig to about 2000 psig, and more preferably within the range from about 500 psig to about 1000 psig, since these pressures permit the use of standard high pressure reactors.
The present process can conventionally be conducted at a temperature within the range of from about 50xc2x0 C. to about 250xc2x0 C., and preferably at from about 100xc2x0 C. to about 200xc2x0 C.
The catalyst herein is at least one hydrogenation catalyst containing a metal selected from the group consisting of rhodium, ruthenium, palladium, and or platinum preferably on a refractory support such as carbon, silica, alumina, aluminosilica, a carbonate such as barium carbonate, diatomaceous earth, and the like. The amount of catalyst employed in the process of this invention can vary widely provided, of course, that a catalytically effective amount of the catalyst is present. Useful amounts of catalyst can range from about 0.05 to about 20 weight percent, and preferably from about 0.5 to about 1 weight percent, based on the weight of the cyanoorganosilane reactant.
It is convenient to add the hydrogenation catalyst to the reactor as a slurry, e.g., in a quantity of the intended principal bis(silylorgano)amine product or in the starting cyanoorganosilane.
The reaction of the starting cyanoorganosilane with hydrogen in the presence of hydrogenation catalyst to provide the desired bis(silylorgano)amine in accordance with this invention can be carried out in known and conventional high pressure reactors. The reactor can be, for example, a fixed bed, stirred-bed or fluidized-bed type reactor. The process can be run as a batch process or as a continuous process. A stirred-bed reactor is preferred. The reaction rate tends to be rapid, and is generally determined by the amount of catalyst, the pressure of the reactor, reaction temperature and related factors as appreciated by those skilled in the art. In general, residence times of from about 0.2 hours to about 5.0 hours provide acceptable results. When the process is run as a batch process, it is generally preferred to use residence times of from about 0.5 to about 3.0 hours accompanied by the addition of hydrogen as it is consumed by the reaction.
The presence of liquid water and/or water vapor is to be substantially avoided as water tends to result in the polymerization of any nitrile and/or aminoorganosilane to a polysiloxane. It is therefore advantageous to purge the reactor, once sealed, with an inert gas such as nitrogen to substantially remove any water that may be present.
The process of this invention can, if desired, be conducted in the presence of an organic solvent as the use of an organic solvent may increase the rate and/or yield of the process without, however, significantly affecting its selectivity for the desired bis(silylorgano)amine. The organic solvent can be a polar or non-polar solvent with a polar solvent, for example, an alkanol such as methanol, ethanol, propanol or isopropanol, being preferred. When using an alkanol solvent, it is preferred that the alkanol correspond to any alkoxy group(s) R1 that may be present in the starting cyanoorganosilane reactant in order to minimize or avoid transesterification. Thus, when the starting cyanoorganosilane contains one or more methoxy groups (e.g., as in the case of the reactants 2-cyanoethyldimethyl-methoxysilane, 2-cyanoethylmethyldimethoxysilane, 2-cyanoethyltrimethoxysilane, 2-cyanoethyldimethoxysilane, 2-cyanoethylphenylmethoxysilane, and 3-cyanopropylmethyl-dimethoxysilane), the alkanol solvent of choice would be methanol. When the process is conducted as a batch process, it is preferred that the solvent be present at from about 5 to about 50 weight percent, and preferably from about 10 to about 20 weight percent, of the total reaction mixture. When the process is conducted as a continuous process and a solvent is utilized, the starting cyanoorganosilane reactant can be diluted in the solvent with the cyanoorganosilane comprising from about 50 to about 95 weight percent, and preferably from about 80 to about 90 weight percent, of the liquid feed to the reactor.
The product bis(silylorgano)amine, together with any coproduced primary aminorganosilane and tris(silylorgano)amine, can be recovered by any known or conventional procedure for separating liquid-solid mixtures and mixtures of liquids, for example, filtration and/or distillation. Any recovered mixture of amine can, if desired, be resolved by known and conventional means to provide the individual amines at high levels of purity.
Bis(silylorgano) amines that can be produced by the present process include, for example, bis[2-(trimethylsilyl)ethyl]amine, bis[2-(dimethylmethoxysilyl) ethyl]amine, bis[2-(methyldimethoxysilyl)ethyl]amine, bis[2-(trimethoxysilyl) ethyl]amine, bis[2-(triethoxysilyl)ethyl]amine, bis[3-(trimethyoxysilyl)propyl]amine, bis[3-(methyldi-methyoxysilyl)propyl]amine, and the like.
Of the following examples, the Comparative Example is presented as a contrast to Examples 1-10 which are illustrative of the process of this invention for obtaining bis(silylorgano)amine. In Tables 1-11 of the examples, the following terms have the indicated meanings:
xe2x80x9cNitrilexe2x80x9d: 2-cyanoethyltrimethoxysilane (CAS No. 2526-62-7; Silquest Y-9802 Silane, OSi Specialties, Sistersville, W.Va.).
xe2x80x9cPrimary Aminexe2x80x9d: 3-aminopropyltrimethoxysilane (CAS No. 13822-56-6; Silquest A-1110 Silane, OSi Specialties, Sistersville, W.Va.).
xe2x80x9cSecondary Aminexe2x80x9d: Bis-[3-(trimethoxylsilyl)propyl]amine, (CAS No. 82985-35-11; Silquest A-1170 Silane, OSi Specialties, Sistersville, W.Va.).
xe2x80x9cTertiary aminexe2x80x9d: tris(trimethoxysilylpropyl)amine (CAS No. 82984-64-3).